Ethylidene diacetate (EDDA) is a valuable intermediate in the production of vinyl acetate (VAc), and considerable interest has been focused on developing improved processes for producing ethylidene diacetate. The commercial success of these improved processes, however, requires a market for the acetic acid (HOAc) which is a coproduct of vinyl acetate production. The acetic acid can be sold, esterified with methanol to methyl acetate (MeOAc or MA), or alkylated with dimethyl ether (DME) to methyl acetate and methanol (MeOH). Methyl acetate (MeOAc), acetaldehyde (AcH), and acetic anhydride (Ac.sub.2 O) are also important as intermediates for the production of other valuable products.
Representative processes for preparing EDDA include German Specification 2,610,035 which discloses a process for producing EDDA wherein the acetic acid obtained as a coproduct can be directly obtained by distillation processes and purified so that it can be used as such or reacted with methanol to form methyl acetate.
British Specification No. 1,538,782 describes a process for producing EDDA wherein dimethyl ether (DME) and/or methyl acetate, carbon monoxide and hydrogen are reacted in the presence of a catalyst system. The reaction preferably occurs in the presence of a Group VIII metal catalyst and a promoter such as an organo-phosphine and/or organo-nitrogen compound.
European Specification No. 35,860 discloses a process for producing EDDA and/or acetaldehyde wherein dimethyl ether or methyl acetate, carbon monoxide and hydrogen are reacted in the presence of a supported palladium catalyst and an halide.
An improved process is described in U.S. Pat. No. 4,319,038 for preparing EDDA and acetic anhydride wherein methyl acetate and/or dimethyl ether, carbon monoxide and hydrogen are reacted in the presence of a quaternary nitrogen, and a manganese or rhenium compound.
European Specification No. 77116 discloses a process for producing EDDA wherein dimethyl ether and/or methyl acetate, carbon monoxide and hydrogen are reacted in the presence of a catalyst system comprising a rhodium compound, a halogen component and a palladium co-catalyst.
European Specification No. 58,442 discloses a process for the coproduction of an alkylidene dicarboxylate and a carboxylic acid by the hydrogenation of a carboxylic acid anhydride in the presence of carbon monoxide and a homogeneous Group VIII metal catalyst together with a chloride, bromide, or iodide and a promoter comprising an organo oxygen, nitrogen, phosphorous, arsenic, or antimony compound having a lone pair of electrons.
U.S. Pat. No. 4,323,697 discloses a process for preparing EDDA wherein methyl acetate and/or dimethyl ether, carbon monoxide and hydrogen are reacted in the presence of a molybdenum-nickel or tungsten-nickel co-catalyst in the presence of a promoter comprising an organo-phosphorous compound or an organo-nitrogen compound. When dimethyl ether is utilized, the reference teaches that a reactor having two reaction zones is preferred. In the first zone, DME is converted by carbonylation to methyl acetate and the second zone is devoted to conducting the EDDA-forming reaction.
U.S. Pat. No. 4,429,150 which discloses a process for producing EDDA wherein methyl acetate and/or dimethyl ether, carbon monoxide and hydrogen are reacted in the presence of a catalyst system comprising a Group VIII metal and a halogen-containing compound in the presence of a sulphur-containing polar solvent, e.g. sulpholane. The reference teaches that organo-phosphorous compounds improve selectivity and increase conversion to EDDA.
An integrated process for the production of synthesis gas is described in U.S. Pat. No. 4,430,096 wherein one or more organic compounds are converted into hydrogen and carbon monoxide by partial oxidation in the presence of steam and/or carbon dioxide. The heat for the reaction is provided by direct heat exchange with products from the gasification of coal with oxygen and steam.
U.S. Pat. No. 4,843,170 discloses a process for preparing vinyl acetate wherein dimethylacetal and acetic anhydride are converted to EDDA and methyl acetate in one of the steps.
U.S. Pat. Nos. 4,810,821 and 5,117,046 disclose the synthesis of ethylidene diacetate by reacting hydrogen and an ether such as dimethyl ether in a catalyzed reactor system. Several different catalyst systems are used to promote the reactions. It is specifically taught that CO.sub.2, if present in the reaction system, is an inert diluent or impurity which does not react with other components in the system.
The preparation of dimethyl ether from synthesis gas in a single stage liquid phase reactor containing solid methanol synthesis and methanol dehydration catalysts slurried in an inert oil is disclosed in European Patent Application 0 324 475 A1, in the article entitled "Single-step Synthesis of Dimethyl Ether in a Slurry Reactor" by J. J. Lewnard et al in Chemical Engineering Science Vol. 45, No. 8, pp. 2735-2741, 1990, and in U.S. Pat. No. 5,218,003.
EDDA thus can be produced by several different process sequences according to the prior art. There is need for an improved integrated process for producing EDDA from synthesis gas with controlled coproduction of acetic acid, and in specific cases with minimum coproduction of acetic acid, while simultaneously maximizing carbon utilization in the synthesis gas feed. In addition, there is need for an improved method for producing vinyl acetate from EDDA with minimum coproduction of acetic acid. Further, the coproduction of the valuable compounds methyl acetate and acetic anhydride is desirable under certain market conditions. The invention described in the following specification and defined by the appended claims provides a new integrated process which fulfills these needs.